There has been considerable interest in designing new concrete structures and strengthening existing concrete structures using fiber reinforced polymers (FRP). Two basic types of FRP exist: carbon (CFRP) and glass (GFRP). FRP materials exist in two forms (unidirectional or bi-directional).
FRP materials provide linear elastic responses under tension loads. In infrastructure applications, nonlinear behavior is important as it allows ductile (non-sudden) failure of structures which is required by most design codes worldwide. The absence of ductility (sudden and brittle failure) at low strains has hindered the widespread use of FRP in civil infrastructure.
Hybrid FRP systems have been developed and have shown the ability to provide nonlinear behavior. However, these systems require a combination of multiple types of fibers (not mono-type) which make hybrids expensive, cumbersome and unattractive for field applications. Failure strain of hybrid fibers has been limited to 3% which does not truly represent ductile behavior.
Moreover, reinforced and pre-stressed concrete infrastructures built in the 1960's and 1970's and are now observing severe deterioration due to corrosion of conventional steel reinforcement. Corrosion of steel typically results from the exposure to aggressive environments (e.g. freeze and thaw cycles) and the use of de-icing salt. Several techniques such as epoxy coated steel bars have been developed to combat corrosion. While these techniques have been able to reduce the rate of corrosion, they have not been able to eliminate the corrosion problem entirely.
There has been considerable interest in designing new concrete structures and strengthening existing concrete structures using FRP. FRP composites offer high strength and low weight, non-corrosiveness, and flexibility in design. Therefore, they represent ideal alternatives to conventional steel reinforcement. Two basic types of FRP exist in structural concrete applications: carbon (CFRP) and glass (GFRP). FRP composites can also be manufactured in different forms such as unidirectional or bi-directional materials. However, the absence of ductility associated with the use of FRP composites has hindered the widespread adoption of FRP composites in civil infrastructure. The absence of ductility is attributed to the linear elastic response of the FRP composite under tension loads. In infrastructure applications, nonlinear behavior of structural components is very important to avoid brittle (catastrophic) failure of structures which is required by most design codes worldwide.